At the Open Network Summit conference here, Andre Fuetsch, AT&T senior vice president, Architecture & Design, said the economics of commodity bare metal switching, as well as the scale, performance and programmability, make it appealing for the carrier to sell into the customer premises.

"Cost is one of the biggest drivers but it's also flexibility, more control," Fuetsch said later during an interview with Network World. "Typically, customers would buy a particular vendor's hardware box and they would have to run their software. By having a more open, flexible box, that allows the customer to choose what particular VNF (virtualized network function) they run: one supplier's firewall, one supplier's load balancer, one supplier's virtualized router."

Fuetsch said white box switches on the customer premises could also run applications, like a virtualized IP PBX.

"So at the CPE, these boxes are extremely flexible, very scalable, they have great economics, and we believe customers are going to want them," Fuetsch said.

The switches will run a uniform operating system and protocol stack, ostensibly defined and/or developed by AT&T, that will also run in the AT&T cloud for scale and operational simplicity, Fuetsch said. Customers will then be able to change VNFs that run on top of it, whether the software stack is on premises or in the AT&T cloud.

"In order to sell a service with the right performance, reliability and to put our stamp of approval on it, we have to have some control over the stack that it's running on," Fuetsch said.

AT&T is also looking at extending SDN and NFV "down the stack" into Layer 1 functions such as optical transport and access. Reconfigurable optical add/drop multiplexers are proprietary and rigid, he says, so software programmability would enhance configurability and provisioning.

In access, SDN and NFV can be used to offer virtualized optical line termination for fiber-to-the-home deployments based on Gigabit Passive Optical Networks. Indeed, AT&T is looking at ON.Lab's ONOS SDN controller, which AT&T helped define, for that specific function, Fuetsch says.

As for AT&T's own internal SDN transformation of its service network, Fuetsch says the carrier is 5% of the way along on its goal of 75% virtualization by 2020.

"We're building the foundation right now," he says. "Once we build in the automation and start maturing our sandbox our incubation and certification environment next year in 2016 we will ramp up significantly."

AT&T is keeping score by determining how technically- and production-ready 200 target VNFs are. Once determining which services make the 200 VNF target list legacy services like ATM, frame relay and TDM voice will not AT&T evaluates the degree to which each is virtualized, under SDN control, and integrated into the carrier's Enhanced Controller Orchestration Management Policy (ECOMP) operations management framework.

ECOMP "gives us a greater degree of automation and autonomous control," Fuetsch says.

AT&T Labs developed ECOMP's policy engine. Differentiation is why AT&T developed its own instead of adopting something like OpenDaylight's Group-Based Policy model.

The VNFs also have to be capable of passing live traffic or workloads, he says. Once 75% of those 200 VNFs hit those virtualization, programmability and live traffic prerequisites, AT&T will have hit its 75% virtualization milestone.

But VNF suppliers also have to meet stringent requirements. Of the 10 announced Domain 2.0 suppliers to AT&T's SDN project, only four so far have made the sandbox to put their products through a rigorous set of virtual network guidelines and requirements, Fuetsch said. He declined to say which ones.

And in terms of customer-facing VNF services, AT&T's Network On Demand is an SDN back-ended offering rolled out in 100 markets. It uses Brocade's OpenDaylight-based Vyatta controller as its brains.

AT&T's MVNO service for resellers is based on Affirmed Networks' evolved packet core and controller. All three controllers Affirmed, Vyatta and ONOS might converge onto one overall master controller for the entire service network over time, Fuetsch says.

ONOS might have the inside track.

"OpenDaylight is much more of a grab bag," Fuetsch says. "There are lots of capabilities, a lot more contributions have gone into it. ONOS is much more suited for greenfield. It takes a different abstraction of the network. We see a lot of promise and use cases for ONOS in the access side with a virtualized OLT as well as controlling a spine/leaf Ethernet fabric. Over time ONOS could be the overall global centralized controller for the network. But because we have the existing network brownfield -- we have to coexist" with other controllers. "ONOS is still maturing."

Though leaning heavily towards open source, AT&T is also evaluating roles for Cisco's Applicatiuon centric Infrastructure and VMware's NSX controllers. AT&T is using NSX in its data centers but there could be bigger roles for it and for ACI... or not.

"We haven't gone public with where we are going with those," Fuetsch said. "Going forward with our Domain 2.0 architecture the real question is, who is going to be the main player that we end up using? That is still yet to be announced."

The biggest challenge in AT&T's two year Domain 2.0 SDN/NFV journey has been the change to traditional operational processes, Fuetsch says. Changing the network means changing all of the ways it was previously constructed, operated, managed, expanded and populated.

Also, AT&T combined its network and IT staffs into a 2,000-strong workforce dedicated to Domain 2.0.

"There's a lot of cultural inertia," Fuetsch said. "We've relied on the supply chain to be the integrators. Now that role is shifting to us. That has cultural implications. The network engineer of yesterday has to be a lot more software savvy for tomorrow. Network engineers and IT engineers speak different languages."

But at the same time, it's an exciting time in networking now that it's opening up.

"Its heyday is now," Fuetsch says. "Now that the network is opening up, we can do a lot of incredible things to take advantage. It really is a liberation into software. We're going to see a tremendous acceleration of innovation."

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